1. Field of the Invention
The present invention relates to a semiconductor optical device.
2. Description of the Related Art
Semiconductor lasers are widely used as semiconductor light sources. For example, a semiconductor laser including an active layer such as GaInAs or GaInAsP formed on a GaAs substrate emits a laser beam having an oscillation wavelength range of 0.9 μm to 1.25 μm. In particular, a semiconductor laser having an oscillation wavelength in 0.98 μm band is used as a pumping light source for an erbium-doped optical fiber amplifier (hereinafter referred to simply as “EDFA”), which is an optical amplifier for optical communications in 1.55 μm band. Furthermore, a semiconductor laser having an oscillation wavelength in a 1.017 μm band is used as a pumping light source for a praseodymium-doped optical fiber amplifier (hereinafter referred to simply as “PDFA”), which is an optical amplifier for optical communications in 1.3 μm band.
Nonpatent Publication 1 (Horie et al., “Longitudinal-mode characteristics of weakly index-guided buried-stripe type 980-nm laser diodes with and without substrate-mode-induced phenomena”, IEEE JOURNAL OF QUANTUM ELECTRONICS (2000), vol. 36, no. 12, p. 1454-1461) discloses a semiconductor laser. Patent Publication 1 (WO2004/027950) discloses a semiconductor laser. Patent Publication 2 (Japanese Unexamined Patent Application Publication No. 2001-144371) discloses a semiconductor laser.